The present invention relates to polymeric conjugates of biologically active agents and methods of preparing the same. In particular, the invention relates to the use of extension moieties, which increase the efficiency of the loading of active ingredients onto polymeric carriers.
Over the years, several methods of administering biologically-effective materials to mammals have been proposed. Many medicinal agents are available as water-soluble salts and can be included in pharmaceutical formulations relatively easily. Problems arise when the desired medicinal agent is either insoluble in aqueous fluids or is rapidly degraded in vivo. Alkaloids are often especially difficult to solubilize.
One way to solubilize medicinal agents is to include them as part of a soluble prodrug. Prodrugs include chemical derivatives of a biologically-active parent compound which, upon administration, eventually liberate the parent compound in vivo. Prodrugs allow the artisan to modify the onset and/or duration of action of an agent in vivo and can modify the transportation, distribution or solubility of a drug in the body. Furthermore, prodrug formulations often reduce the toxicity and/or otherwise overcome difficulties encountered when administering pharmaceutical preparations. Typical examples of prodrugs include organic phosphates or esters of alcohols or thioalcohols.
Prodrugs by definition are often biologically inert or substantially inactive forms of the parent or active compound. The rate of release of the active drug, i.e. the rate of hydrolysis, is influenced by several factors but especially by the type of bond joining the parent drug to the modifier. Care must be taken to avoid preparing prodrugs which are eliminated through the kidney or reticular endothelial system, etc. before a sufficient amount of hydrolysis of the parent compound occurs.
Incorporating a polymer as part of a prodrug system has been suggested to increase the circulating life of a drug. A brief overview of some previous work in the field is presented below.
Ohya, et al., J. Bioactive and Compatible Polymers Vol. 10 January, 1995, 51-66, discloses doxorubicin-PEG conjugates which are prepared by linking the two substituents via various linkages including esters. The molecular weight of the PEG used, however, is only about 5,000 at most. Thus, the in vivo benefits are not fully realized because the conjugates are substantially excreted prior to sufficient linkage hydrolysis.
Commonly-assigned PCT publication WO96/23794 describes bis-conjugates in which one equivalent of the hydroxyl-containing drug is attached to each terminal of the linear polymer. In spite of this advance, techniques which would further increase the payload of the polymer have been sought.
In another commonly-assigned PCT application, WO99/53951 (the ""951 application), therapeutic polymeric conjugates with double or even greater therapeutic payloads are disclosed. Specifically, the polymers which are substantially linear, are designed to include multifunctional groups on both the alpha and omega terminus which are adapted for receiving up to four or more equivalents of a biologically active agent. Further work in this field has been done to address the problems which can occur when attempting to achieve complete or stochiometric loading of some active ingredients onto the multi-armed polymers. In particular situations, it has been found that it would be desirable to be able to provide more predictable and reproducible high degrees of loading. Such can be the case especially when steric hindrance or the molecular shape of the active ingredient reduces the likelihood of relatively complete loading of each multi-armed terminal group.
Commonly assigned U.S. Ser. No. 09/404,705 discloses still further bifunctional polymer conjugates. In particular, the application describes bifunctional polymers containing one equivalent of ara-C or a related anti-metabolite attached on each terminal. While reproducible and complete loading of such polymers is less of a concern than with the multi-armed terminal groups described above, improvements were nonetheless sought. The contents of each of the above-mentioned commonly-assigned patent applications and PCT international applications is incorporated herein by reference.
Thus, there continues to be a need to provide additional technologies for forming polymeric prodrugs of therapeutic moieties. The present invention addresses this need.
In one aspect of the invention, compounds of Formula (I) are provided: 
wherein:
G is a linear or branched polymer residue;
Y1 and Y2 are independently O, S, or NR9;
M1-M3 are independently O, S, or NR10;
M4 is X or Q;
wherein X is an electron withdrawing group and Q is a moiety containing a free electron pair positioned three to six atoms from C(xe2x95x90Y2);
B is a residue of an amine-containing moiety or a residue of a hydroxyl-containing moiety;
R1-10 are independently selected from the group consisting of hydrogen, C1-6 alkyls, C3-12 branched alkyls, C3-8 cycloalkyls, C1-6 substituted alkyls, C3-8 substituted cycloalkyls, aryls, substituted aryls, aralkyls, C1-6 heteroalkyls and substituted C1-6 heteroalkyls;
a, b, c, d, e, f, g, h, i and n are each independently zero or a positive integer.
In preferred embodiments, G is a bifunctional polymer residue based on polyalkylene oxides such as poly(ethylene glycol) (PEG) and M1-M3 are O or NR10 and R10 is preferably H. M4 is also preferably O or NR10, where R10 is preferably H.
In preferred aspects of this invention, the polymeric residue is substituted on both the proximal and the distal portion to provide the compounds of the formula: 
where all variables are as previously defined.
When B is a residue of a hydroxyl-containing moiety or an amine-containing moiety, each B is attached via a preferably hydrolyzable linkage which attaches to the polymer residue terminus.
Examples of hydroxyl-containing moieties for which one or more of improved aqueous solubility, decreased antigenicity, prodrug and/or controlled release delivery is desired include chemotherapeutic compound residues such as anti-fungal compounds, including hydroxyl-containing triazoles, hydroxyl-containing echinocandins, hydroxyl-containing pneumocandins, etc, anti-cancer compounds such as camptothecin, paclitaxel, etoposide, anti-cancer platinum compounds containing OH groups, floxuridine or podophyllotoxin.
Examples of amine-containing moieties for which one or more of improved aqueous solubility, decreased antigenicity, prodrug and/or controlled release delivery is desired include antimetabolites such as Ara-C or gemcitabine. In still further embodiments, other oncolytic agents, non-oncolytic agents such as anti-inflammatory agents, including steroidal compounds, protease inhibitors such as AZT, as well as therapeutic low molecular weight peptides such as insulin are also contemplated.
For purposes of the present invention, the term xe2x80x9cresiduexe2x80x9d shall be understood to mean that portion of a biologically active compound which remains after the biologically active compound has undergone a substitution reaction in which the prodrug carrier portion has been attached.
For purposes of the present invention, the term xe2x80x9calkylxe2x80x9d shall be understood to include straight, branched, substituted, e.g. halo-, alkoxy-, and nitro-C1-12 alkyls, C3-8 cycloalkyls or substituted cycloalkyls, etc. xe2x80x9cHaloxe2x80x9d shall be understood to include, for example, fluoro, chloro, bromo, iodo.
For purposes of the present invention, the term xe2x80x9csubstitutedxe2x80x9d shall be understood to include adding or replacing one or more atoms contained within a functional group or compound with one or more different atoms.
The term xe2x80x9csufficient amountsxe2x80x9d for purposes of the present invention shall mean an amount which achieves a therapeutic effect as such effect is understood by those of ordinary skill in the art.
One of the chief advantages of the compounds of the present invention is that the prodrugs have a more predictable degree of loading which is achieved by using the extender (or spacer) moieties described herein between the polymer residue ends and the parent therapeutic molecules. The substantially uniform polymeric conjugates are thus easy to analyze and are highly reproducible. The rate of hydrolysis is also predictable and reproducible from batch to batch. Still, a further advantage is that in certain preferred embodiments, in which the polymer portion has a molecular weight of from about 20 to about 50 kDa, conjugates containing anti-tumor agents are believed to passively target tumors and thus enhance the effectiveness of the anti-tumor parent compound on solid tumors. While applicants are not bound by theory, it is believed that tumor proteases, alone and/or in combination with peptidases, cleave the covalent linkage between the polymer and active agent, thus freeing the parent active agent within the tumor.
Methods of making and using the compounds and conjugates described herein are also provided.